INFLUENCE OF SURFACE ATTITUDE AND CURVATURE SCALING ON DISCRIMINATIONOF BINOCULARLY PRESENTED CURVED SURFACES

We report on the ability of human observers to discriminate local seco nd-order shape of quadratic stereo-defined surfaces. Local second-orde r shape can be specified by two parameters: the curvedness (a scale-de pendent quantity describing overall curvature of a shape) and the shap e index (a scale-independent quantity describing the shape's appearanc e). We measured shape index discrimination thresholds of shapes subjec t to attitude and curvedness transformations. Results show that neithe r slant nor curvedness manipulations affect or bias observers' judgeme nts of surface shape. Furthermore, ideal detector simulations show tha t observers do not perform optimally: they do not exploit all availabl e information.